Snap acting switch blade



March 5, 1963 E. A. KURZ 3,080,464

SNAP ACTING SWITCH BLADE Filed Aug. 6, .1959

' INVENTOR [TOM/42a 4. KIIPZ or; OFF

M: ATTORNEYS H BY kiwi- United States Patent 3,08%;564 SNAP ACTING SWITCH BLADE Eward A. Kara, Craniord, NJ assiguor to Tung-fiol Electric inc, a corporation of Delaware Filed Aug. 6, 1959, Ser. No. 832,018 3 Claims. (Cl. 290-422) The present invention relates to snap acting elements for use in switches, flashers, relays or the like and comprises a novel snap blade which is of simple construction, has positive action in operation, good contact pressure characteristics and which is not subjected to high stresses during snap action.

Briefly the new element comprises a sheet or blade of spring metal, such as nickel, spring steel or the like, which may be of generally rectangular shape and which is fixedly mounted near one side edge substantially at the mid point thereof. Near the opposite free edge, the blade is stressed, as by crimping, to cause the portion adjacent that edge to assume a curved shape. A contact is centrally mounted on the concave side of the stressed portion of the blade. Adjacent the mounted edge of the blade a control member, such as an expansible wire or ribbon, is secured under tension to the blade to how the same oppositely to the bow resulting from the stress introduced at the free edge. Variation in tension of the wire or ribbon with change in temperature varies the degree of curvature of the blade and causes the contact carrying part of the blade to reverse its curvature with a snap action. A fixed contact is positioned to be engaged under pressure by the blade carried contact when the tension in the pull strip is at a minimum.

For a better understanding of the invention and of the preferred embodiment thereof reference may be had to the accompanying drawing of which:

FIG. 1 is a perspective view of a snap acting blade embzodyin g the invention and shown in contact open position;

F165. 2 and 3 are diagrams representing transverse sections of the snap blade of P16. 1 taken along the lines 2-2 and 3-3;

FIG. 4 is a diagrammatic longitudinal section of the blade of FIG. 1;

FIGS. 5 and 6 and 7 are diagrammatic sectional views corresponding to the sectional views of FIGS. 2, 3 and 4, respectively, but showing the blade in contact closing position; and

FIG. 8 is a graph showing the contact force characteristic of the device of the invention when operating in a flasher circuit.

In the drawing the new snap blade 2 is shown as of generally square or rectangular shape. A pair of ribs 4 are formed in the blade adjacent one side thereof and perpendicular thereto. These ribs crimp the metal of the blade and tend to cause it to curve about an axis parallel to the ribs. Adjacent the opposite side of the blade is a pull wire or strip 6 the ends of which are fastened under tension to the blade to cause the blade to curve about the same axis but in a direction opposite to the direction of curvature introduced by the ribs 4. When the pull strip is cold, that is when the tension therein is a maximum, the curvature introduced thereby tends to reverse the curvature of the opposite end of the blade. When the pull strip is expanded by heat, the tension therein is sufficient to prevent reversal of curvature at the adjacent end of the blade but insufiicient to prevent the other of the blade from assuming the direction of curvature imposed thereon by the ribs 4. Consequently, when the pull strip is cold, the blade 2 as shown by FIGS. 1, 2, 3 and 4 is bowed concavely upward but, because of the bias introduced by the ribs 4, the extent of curvature varies from a maximum at one end of the blade to a at the Patented Mar. 5, 1963 other end of the blade. This is apparent from a comparison between FIGS. 2 and 3, showing greater curvature in the neighborhood of pull strip 6 and lesser curvature in the neighborhood of the ribs 4. The blade 2 is mounted near the edge remote from the ribs 4 on any suitable conductive support such as the post 8 of FIG. 1 which in turn is mounted on a suitable insulating base 10 for connection to an external circuit. On the under surface of the ribbed edge of the element is mounted a contact 12 which, in the position of the element shown in FIGS. 1 and 3, overlies but does not engage a fixed contact 14 supported on the base it and adapted for connection through a post 16 to an external circuit. In order to vary the tension in the pull strip 6 a heater coil 13 of insulated wire is wound about the strip 6. The ends 20 of the coil are connected to a suitable heating circuit (not shown).

With the above described construction, when coil 18 is energized it heats the ribbon or strip 6 which expands. The consequent reduction in tension reduces the curvature of the mounted end of the blade. The bias introduced into the blade by the ribs 4, under such reduction in tension of the pull strip, causes the free end of the blade to snap into contact closing position shown in FIGS. 5 through 7. The reversal in curvature of the free end of the element takes place with a snap action causing immediate build up of contact pressure. When the current to the heating coil 18 is interrupted the strip 6 cools and contracts and hence, when the stress introduced by the pull strip reaches a predetermined value, the free end of the blade snaps back into the position shown in FIGS. 1 through 4 with consequent abrupt opening of the contacts.

During the above described operation there is no reversal of curvature at the control end, namely the end carrying the pull strip 6 and therefore the welds between P the blade and pull strip are subjected to less stress than would be the case if reversal of curvature took place in this part of the blade.

The above described device can be incorporated in any of the known types of flasher or relay circuits. In the case of a flasher circuit the closure of contacts could, for example, operate to shunt the heating coil and thereby initiate contraction of the pull strip with ultimate opening of the contacts and reenergization of the heating coil. In the case of a relay, the fixed and movable contacts of the device could be in a circuit separate from that of coil 18 so as to be controlled by control of current to the coil 18.

To illustrate the square wave characteristic of the contact pressure of the blade there is shown in the diagram of FIG. 8 a graph representing contact pressure as a function of time when the device is connected to operate as a flasher. The graph shows the abrupt increase in contact pressure upon snapping of the device to cont-act closing position and the maintenance of substantially full contact pressure up to the moment when the blade snaps to contact open position.

The invention has now been described with reference to a single embodiment thereof. Obviously various changes in the particular shape of the parts and of the control means therefor could be made without departing from the spirit of the invention or the scope of the accompanying claims. For example, although the snap element or blade has been shown as rectangular, such shape is not essential. The corners of the free edge could be truncated or curved if desired. Also, the pull strip, instead of being heated from a separate winding, could be incorporated directly in a heating circuit so as to expand and contract with variation in current therethrough. Other variations will occur to those skilled in the art.

The following is claimed:

1. A snap acting switch blade comprising a sheet of spring metal, ribs formed in the sheet extending from, and perpendicular to, one edge thereof, said ribs tending 3 to curve the; portion of the sheet adjacent, that edge about an axis in the sheet perpendicular to that edge, a thermally expansible pull strip secured under tension at its ends to the sheet parallel to said edge and adjacent an edge of the sheet remote from that having the ribs extending therefrom, said pull stripintroducing a cu rvaa tu re-into saidsheet opposite to that introduced by said ribsandabout the same axis, and means for heating said. strip to reduce the tension therein.

2 The snap acting switch blade, according to claim 1' ineludin g means for mounting said sheet substantially on the axis of curvature and adjacent said pull strip, a contact secured to saidsheet substantial-1y on said axis on the concave side of the curvature introduced by said ribs and adjacent the edge having the ribs formed therein, and

a fixed contact positioned for engagement under pressure References Qited. the file of this patent UNITED STATES PATENTS 2,299,562 Burch Oct. 20, 1942 2,615,106,: chmi inger r r Oct. 21, 1,952 2,712,044 Welsh June 28, 1955 2,870,291; Welsh r Jan. 20, 1959 2,8ZO- 292 w 1s Jan. 20, 1959 2,818 0 Uhl "a? M r.- 17, 195 

1. A SNAP ACTING SWITCH BLADE COMPRISING A SHEET OF SPRING METAL, RIBS FORMED IN THE SHEET EXTENDING FROM, AND PERPENDICULAR TO, ONE EDGE THEREOF, SAID RIBS TENDING TO CURVE THE PORTION OF THE SHEET ADJACENT THAT EDGE ABOUT AN AXIS IN THE SHEET PERPENDICULAR TO THAT EDGE, A THERMALLY EXPANSIBLE PULL STRIP SECURED UNDER TENSION AT ITS ENDS TO THE SHEET PARALLEL TO SAID EDGE AND ADJACENT AN EDGE OF THE SHEET REMOTE FROM THAT HAVING THE RIBS EXTENDING THEREFROM, SAID PULL STRIP INTRODUCING A CURVATURE INTO SAID SHEET OPPOSITE TO THAT INTRODUCED BY SAID RIBS AND ABOUT THE SAME AXIS, AND MEANS FOR HEATING SAID STRIP TO REDUCE THE TENSION THEREIN. 